PHYSIOS OF THE GLOBE. 109 



from that which produces the variation itself, and that this 

 cause acts, when there are no sun-spots, in the same way as, 

 though with less intensity than, when the spots have their 

 maximum frequency and area ; therefore the magnetic vari- 

 ations are not due to the sun-spots, although there is a gen- 

 eral agreement in their respective changes. No theory which 

 has yet been suggested connecting the two phenomena seems 

 to him to be satisfactory. 



De Parville presents to the French Academy of Sciences 

 a very novel application of the telephone, by means of 

 which he proposes to determine the direction of the magnet- 

 ic meridian. He states that when in the ordinary telephone 

 we replace the short bar magnet by a rod of soft iron, at 

 least one meter long, the apparatus still transmits the sounds, 

 but with an intensity which varies according to the orienta- 

 tion of the rod. The maximum intensity of the sound which 

 is transmitted to the receiver corresponds to the orientation 

 of the transmitter in the direction of the magnetic needle. 

 The sound is heard more or less completely, when the tele- 

 phone is placed in a plane perpendicular to the magnetic me- 

 ridian. By a proper apparatus, he is thus able to determine 

 the variations of magnetic intensity at different azimuths. 



Capt. F. J. Evans read before the Geographical Associa- 

 tion of London, in March, a discourse on Terrestrial Mag- 

 netism and its Secular Variations. After fully recounting 

 the history of the progress of our knowledge, and the the- 

 ories of Halley, Hansteen, Gauss, Sabine, etc., he explained 

 some of the results of the magnetic observations of the 

 Challenger Expedition ; and showed the necessity of remod- 

 elling our views, or rather of continuing our search for the 

 ultimate explanation of terrestrial magnetism. The evi- 

 dences of change in the total intensity of magnetic force are 

 very slight, and point to a sensible constancy in the north- 

 ern hemisphere ; but in the southern hemisphere such pro- 

 gressive change is just now going on very rapidly. The 

 C/udlenger observations show that at Valparaiso the total 

 intensity has in fifty years diminished one sixth ; in Mon- 

 tevideo, one seventh; in the Falkland Islands, one ninth; 

 in Bahia and Ascension, one ninth. The area of diminish- 

 ing force extends from Tahiti to St. Helena, and from the 

 Equator to the Cape of Good Hope. 



